This invention concerns a method to roll strip and plate and the rolling line which performs this method.
To be more exact, the invention arranges to produce strip or plate by starting from thin slabs consisting of steel or of a metallic alloy and produced by means of continuous casting, thus obtaining a product of a high surface and internal quality.
Thin slabs to which the invention is applied have a thickness between 70 and 110 mm.
The rolling line according to the invention is able to tend a casting machine having at least one line.
In the-case of two casting lines, they are fed at the same time, thus optimising the yield and efficiency of the plant and especially the yield of the rolling train.
In the field of rolling and, in particular, in the production of strip and/or plate, the problems are well known which are encountered by producers in obtaining a product of a high quality and in using at the same time a production line characterised by great functionality, versatility, good use of space and by fast and reduced times spent on corrective work for maintenance and replacement.
The state of the art also covers rolling lines, such as that in European patent application No. 951028.81.0 for instance, which are fed alternately by two or more continuous casting machines; these lines normally include systems for transferring the products from the casting line or lines positioned offset from the rolling line.
The transfer systems are normally obtained with modular elements forming part of a furnace performing temperature maintenance and possible heating of the segments of slabs coming from the relative continuous casting line.
In these rolling plants associated with at least two continuous casting machines one furnace is normally in-line and feeds the segments of slab to the rolling train, while the other furnace acts as a buffer store and maintains the temperature of the segments until they are sent to the rolling train.
In such a case, since the rolling train and continuous casting machine normally work at different speeds, interruptions of the feed to the rolling train take place between one segment of slab and the next one.
This fact not only entails a reduction of the yield of the whole plant but also involves the great risk of damage and wear to the rolling rolls owing to continuous alternate stresses arising from a very discontinuous processing.
Moreover, complex and bulky systems are required for the buffer store and for traversing so as to contain and to transfer the segments which gradually accumulate on the casting line acting as a buffer store at that moment.
Furthermore, the traditional plants include two distinct systems for feeding the molten metal to the mould, each system being equipped with its own ladle.
This involves a great overall bulk, the possibility of contacts between the two systems, less space for possible work to maintain and/or replace the components and also working difficulties connected with the discharge of the molten metal into the two different mould systems.
Another aspect which characterises the plants of the state of the art concerns the descaling systems included in-line.
The plants of the state of the art normally include descaling systems with stationary water walls positioned at the outlet of the temperature-maintaining and/or heating furnaces.
These embodiments not only entail a great waste of water but also are incapable of eliminating all the scale which forms on the surface of the products being rolled, especially in the normal case in which the scale formed consists mainly of hard oxides owing to the low speed of feed and the high temperature.
If the segment of slab entering the furnace has on its surface a great quantity of scale, the layer of scale increases considerably within the furnace and, in view of its content, is very difficult to remove.